Retatrutide: The Triple-Agonist Weight-Loss Drug (2026 Guide)
Retatrutide is Eli Lilly's investigational triple agonist, hitting the GLP-1, GIP, and glucagon receptors in one weekly injection. Its Phase 3 program, TRIUMPH, reported the highest weight loss yet seen in an obesity trial of a non-surgical drug: 28.3% at 80 weeks on the 12 mg dose. This guide covers what the trials actually show, how retatrutide is dosed, its safety profile, and where it stands with the FDA as of 2026.
How the triple mechanism works
Retatrutide activates three receptors. GLP-1 and GIP drive appetite suppression and improve insulin response, the same pathways behind semaglutide and tirzepatide. The third target, the glucagon receptor, adds a different lever: it raises energy expenditure and mobilizes fat, rather than only reducing intake. See our full mechanism breakdown for how the three pathways combine.
Glucagon activation carries a theoretical risk of worsening blood sugar, since glucagon raises glucose. Retatrutide is balanced to fire all three receptors together rather than glucagon alone, and in trials glycemic control improved rather than deteriorated, including in participants with type 2 diabetes.
TRIUMPH-1: the current Phase 3 evidence
Retatrutide's efficacy is now defined by the Phase 3 TRIUMPH program, not the earlier Phase 2b study. TRIUMPH-1 (NCT05929066) enrolled 2,339 adults with obesity, or overweight plus a weight-related condition, without diabetes. Topline results were announced May 21, 2026, with full data presented at the American Diabetes Association Scientific Sessions in June 2026.
Mean weight loss at 80 weeks was 19.0% on 4 mg, 25.9% on 9 mg, and 28.3% on 12 mg. A prespecified 104-week extension in 532 participants with baseline BMI of 35 or higher reached 30.3% on the 12 mg dose, a level in the range associated with bariatric surgery. A nested substudy in participants with severe obstructive sleep apnea cut the apnea-hypopnea index by 60.6% at 12 mg. Eli Lilly has also reported wins in additional Phase 3 trials (TRIUMPH-2 and TRIUMPH-3) covering type 2 diabetes and other populations.
| Dose (weekly) | Mean weight loss | Duration |
|---|---|---|
| 4 mg | 19.0% | 80 weeks |
| 9 mg | 25.9% | 80 weeks |
| 12 mg | 28.3% | 80 weeks |
| 12 mg (BMI 35+ extension) | 30.3% | 104 weeks |
For a fuller read of these outcomes, see our retatrutide weight-loss guide.
The older Phase 2b data and why 24.2% is superseded
For three years the number attached to retatrutide was 24.2%, from the 48-week Phase 2b trial published in the New England Journal of Medicine in 2023 (n=338, placebo-controlled, no active comparator). At 48 weeks, least-squares mean weight change was -8.7% on 1 mg, -17.1% on 4 mg, -22.8% on 8 mg, and -24.2% on 12 mg, versus -2.1% on placebo. That trial established the dose range and safety signal that TRIUMPH then tested at scale.
The 24.2% figure still circulates widely, but it has been superseded by the larger, longer Phase 3 result of 28.3% at 80 weeks. Anyone citing 24.2% as retatrutide's current efficacy is quoting the older study. The two trials also used different dose sets: 1/4/8/12 mg in Phase 2b versus 4/9/12 mg in TRIUMPH-1.
How it compares to tirzepatide and semaglutide
Across separate Phase 3 trials, retatrutide 12 mg reached 28.3% at 80 weeks, tirzepatide 15 mg reached 20.9% at 72 weeks in SURMOUNT-1, and semaglutide 2.4 mg reached roughly 15% at 68 weeks in the STEP program. These are cross-trial estimates. The drugs were tested in different populations over different durations and have never been compared head-to-head, so the gaps are indirect, not measured differences.
Full breakdowns: retatrutide vs tirzepatide, retatrutide vs semaglutide, and retatrutide vs Ozempic. The practical difference today is availability: tirzepatide and semaglutide are approved and prescribable now, and retatrutide is not.
Dosing in trials
Retatrutide is a once-weekly subcutaneous injection, titrated up gradually to limit gastrointestinal side effects. Phase 2b used roughly 4-week steps through 1, 4, 8, and 12 mg; TRIUMPH-1 used a 4, 9, and 12 mg set with 12 mg as the maintenance target. No dose above 12 mg has been studied in humans. Because retatrutide is not approved, there is no official label schedule yet. See our dosing guide and dosage calculator for the trial escalation schedules, and tirzepatide dosing for a comparison.
Side effects and safety
Gastrointestinal effects are the dominant category and scale with dose. In TRIUMPH-1, nausea was reported by about 28.6%, 38.4%, and 42.4% of the 4 mg, 9 mg, and 12 mg groups versus 14.8% on placebo; vomiting ran from 10.6% up to 25.3% versus 4.8%. Symptoms clustered during titration rather than at steady state, and the 80-week data did not surface a new class of adverse events beyond what the 48-week Phase 2b study showed.
Discontinuation for adverse events was 4.1%, 6.9%, and 11.3% across the three doses versus 4.9% on placebo, so the lowest dose was tolerated about as well as placebo while the top dose roughly doubled the placebo rate. Retatrutide also raises resting heart rate, consistent with the incretin class. Our side-effects guide covers management and the rarer risks.
Regulatory status and availability
Retatrutide is not FDA approved as of 2026 and remains investigational. Eli Lilly has said it plans to submit its application to the FDA in early 2027, after completing the Phase 3 TRIUMPH program; the company pushed the timeline out from an earlier 2026 target while it gathered more manufacturing and quality-control data. There has also been a public dispute with the FDA over whether retatrutide should be regulated as a biologic, which affects the submission pathway.
A limited early-access program began in 2026, but the drug is not broadly prescribable. For the current timeline see our FDA approval tracker and how to get retatrutide. Anyone weighing options now is comparing an available drug against one that is still in trials.
Cost expectations
There is no set price because retatrutide is not on the market. Projections generally put a brand-name triple agonist in the range of current GLP-1 drugs, roughly $1,000 to $1,500 per month before insurance, with real pricing dependent on launch strategy, competition, and coverage. Our cost analysis walks through the assumptions. Treat any firm "retatrutide price" quoted today as an estimate.
Frequently Asked Questions About Retatrutide
Retatrutide is an investigational triple receptor agonist from Eli Lilly that targets three receptors at once: GLP-1, GIP, and glucagon. Semaglutide acts on GLP-1 only and tirzepatide on GLP-1 and GIP; retatrutide adds glucagon-receptor activity, which raises energy expenditure on top of the appetite suppression the other two rely on. It is given as a once-weekly subcutaneous injection.
In the Phase 3 TRIUMPH-1 trial (n=2,339, NCT05929066), announced May 21, 2026, mean weight loss at 80 weeks was 19.0% on 4 mg, 25.9% on 9 mg, and 28.3% on 12 mg. A prespecified 104-week extension in 532 participants with baseline BMI of 35 or higher reached 30.3% on 12 mg. The earlier Phase 2b trial (NEJM, 2023, n=338) reported up to 24.2% at 48 weeks on 12 mg; that figure is now superseded by the larger, longer Phase 3 result.
As of 2026 retatrutide is not FDA approved and remains investigational. Eli Lilly has said it plans to file its application with the FDA in early 2027; the original 2026 target slipped while the company gathered additional manufacturing and quality-control data. A limited early-access program began in 2026. Note that Mounjaro is tirzepatide, a separate Eli Lilly drug, and is not a brand name for retatrutide.
On weight loss alone the Phase 3 numbers favor retatrutide: 28.3% at 80 weeks on 12 mg in TRIUMPH-1, versus 20.9% for tirzepatide 15 mg at 72 weeks in SURMOUNT-1 and roughly 15% for semaglutide 2.4 mg at 68 weeks in the STEP program. But none of these drugs have been tested against each other in the same trial, so those gaps are cross-trial estimates, not measured head-to-head differences. Tirzepatide and semaglutide are also approved and available today; retatrutide is not.
Gastrointestinal effects dominate and scale with dose. In TRIUMPH-1, nausea was reported by about 28.6%, 38.4%, and 42.4% of the 4 mg, 9 mg, and 12 mg groups versus 14.8% on placebo; vomiting ran 10.6% to 25.3% versus 4.8%. Discontinuation for adverse events was 4.1%, 6.9%, and 11.3% across the three doses versus 4.9% on placebo, so the top dose roughly doubled the placebo rate. Retatrutide also raises resting heart rate, similar to other incretin drugs.
Retatrutide is a once-weekly subcutaneous injection titrated up over the first months of treatment. The Phase 2b trial tested 1 mg, 4 mg, 8 mg, and 12 mg using roughly 4-week escalation steps; Phase 3 TRIUMPH-1 used a 4 mg, 9 mg, and 12 mg set with 12 mg as the maintenance dose. 12 mg is the highest dose studied in humans. Because retatrutide is not approved, there is no official prescribing schedule yet.
Not through normal prescription channels. Retatrutide has no FDA approval, so it cannot be lawfully marketed or prescribed as a finished drug in the US. Eli Lilly began a limited early-access program in 2026. Research-grade "retatrutide" sold by peptide vendors is not pharmaceutical-grade, is not quality-controlled for human use, and sits outside the trial evidence described here.